posted on 2023-04-17, 17:38authored bySamuel Sutiono, Ioannis Zachos, Leandros Paschalidis, André Pick, Jakob Burger, Volker Sieber
Many platform chemicals
such as 1,2,4-butanetriol (BTO)
are still
derived from petrochemicals. BTO as a versatile compound with applications
ranging from pharmaceutical synthons to plasticizers is of great interest
to be manufactured from renewable resources. Albeit biosynthetic pathways
to produce BTO from pentoses were proposed two decades ago, no studies
have reported production at high yields and titers typically demanded
by chemical industries. In this work, we aimed to tackle this challenge
by combining several strategies. Selection of suitable enzymes and
reaction optimization in a 500 μL lab scale allowed us to achieve
a titer of 1.2 M (125 g/L) (S)-BTO from 180 g/L d-xylose
with a yield >97%. By the addition of an intermediate of the cascade,
we could reduce up to 90% of the original redox cofactor used while
still maintaining a space-time yield (STY) of 3.7 g/L/h. By applying
the same approach, which we term “intermediate boosting”,
we could push the STY to 9.4 g/L/h. After having identified byproduct
formation as a possible bottleneck, we increased production of (S)-BTO
further to 1.6 M (170 g/L), approaching the toxicity level of BTO
at 200 g/L that microorganisms can handle. We demonstrated, however,
that our enzymes were still functional at 300 g/L BTO. Finally, we
proposed several strategies to further increase the titer and yield
of BTO as a feasible alternative to the petroleum-based synthetic
route. This work highlights the importance of a combinatorial approach
to boost the enzymatic biosynthesis of chemicals.